1. Field of the Invention
The invention relates to a fingerprint identifying system, more particularly to a fingerprint identifying system having an improved identification rate.
2. Description of the Related Art
Referring to FIG. 1, a conventional fingerprint identifying system 1 includes an image-capturing unit 11, a finger press plate 12, a light-diffusion plate 13 disposed between the image-capturing unit 11 and the finger press plate 12, and a plurality of light sources 14 disposed below the light-diffusion plate 13. The finger press plate 12 has a press surface 121 for disposing a finger (A) thereon. The light-diffusion plate 13 guides the light from the light sources 14 so as to serve as a planar light source transmitting light toward the finger press plate 12, and has a through hole 131 in alignment with the image-capturing unit 11. When the light from the light-diffusion plate 13 illuminates the finger (A) disposed on the press surface 121 of the finger press plate 12, the light illuminating the grooves of the finger (A) is reflected from the press surface 121 to the image-capturing unit 11 through total internal reflection, and the light illuminating the ridges of the finger (A) will be absorbed by the finger (A) so as to create a fingerprint image, which is dark where there are ridges and bright where there are grooves.
However, since there is the through hole 131 in the light-diffusion plate 13, the light illuminating the center portion of the finger (A) is less than that illuminating the remainder of the finger (A). Therefore, the center portion of the finger (A) has an unsatisfactory illumination, which results in an unsatisfactory fingerprint identification rate.
Referring to FIG. 2, a fingerprint identifying system 2 disclosed in U.S. Pat. No. 5,177,802 includes an image pickup device 21, a lightguide plate 22 disposed above the image pickup device 21, and two light sources 23 disposed at two sides of the lightguide plate 22, respectively. When light emitted from the light sources 23 enters into the lightguide plate 22, the light is guided by the lightguide plate 22 to a finger (B) through total internal reflection. The light is then reflected on the contour of the fingerprint pattern of the finger (B) and reaches the image pickup device 21 to form an image of the fingerprint.
However, in the fingerprint identifying system 2, in order to permit the light from the light sources 23 to be guided by the lightguide plate 22 at accurate angles for creating the total internal refection, the assembly angle of the light sources 23 relative to the lightguide plate 22 is strictly limited. Therefore, the yield of the fingerprint identifying system 2 may be reduced due to an error of the assembly angles of the light sources 23 relative to the lightguide plate 22.